924Board.org

[Euro924S2]

Hi Guys. Over the past 2 years I've been fitting an M90 supercharger from an Aston Martin DB7 (short nose charger) to a stock rebuilt 931 euro engine (s2 with 8.5:1 CR). The engine is fully rebuilt with stock parts with the exception of total seal piston rings rather than conventional stock rings. The original standard size cast 931 pistons were in good condition and the block only needed a re-hone to remain in tolerance.

You might remember my M62 supercharged engine made 232bhp and 231ft/lb but this was on a stock NA clutch which became contaminated by excessive oil blow by because of worn valve stem seals. The plan was to simply transfer the M62 parts across to freshly rebuilt motor but when this M90 became available, I hatched a new plan!

The m62 ran hot at cruise, off boost, speeds because of a twin throttle setup needed to eliminate lag because of a long intake track and 951 intercooler. I even managed to seize the first 62 charger on the motorway on a hot day when off boost because of this hot running state.

With the M90 being much shorter because the bypass valve is a separate unit rather than incorporated into the charger housing like on the 62, I was able to mount it sideways, giving enough room for an inlet manifold with integrated charge cooler radiator.

This reduced throttle volume meant t he twin throttles were ditched and cool temps are achieved!

I'll post up some current pics and then back track to the build pics for those that are interested!

I've not dyno'd it yet as I've just completed the 1k mile engine run in and so now I'm ready to do some high end mapping and then I'll take it to the dyno to perfect and get some numbers. It's hitting 1.5bar from the point of WOT though, so I'm hoping for some good numbers! (The 232bhp on the m62 was at 1bar)








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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

[Raceboy]

This is very-very cool build!

Does it builds 1.5bars already from down low in rpm range? What about detonation in max torque area?
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[Rasta Monsta]

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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Euro924S2]

Thanks guys. I've not stamped the throttle from 900rpm but I accelerated through a set of traffic lights in the wrong gear at about 1.5krpm, heard knock and looked at the boost gauge to see over 1bar boost. I posted a data log on the UK forum of a short pull up a hill to demonstrate the boost and temperatures etc and was laughed at because I logged 100% for all of 0.9s before I backed out of the throttle!! I'd like to explain it was multi-factorial!! Is only done 600miles on the rebuilt engine, I was already close to breaking the speed limit and most importantly I was a bit scared it was about to explode!! These engines sound pretty tortured when boosted quite so high!!

Ignition timing tuning is still in progress since it takes 2 people on the road - 1 to drive and the other to work the laptop, but my brother has been busy so it's a primitive log ATM. The charge cooler seems to work really well keeping the inlet temps to less than 40*C despite charger outlet temps of around 110*C in ambient temperatures of 25*C (good summers day in the UK!). My exhaust gas temps were all pretty good at 650*C ish (I have 1sensor in each exhaust manifold runner as it leaves the head).

I'm on holiday in Greece ATM so I can't post my logs etc but I'll post again ASAP with my setup as I have a modified coolant system etc to help explain my optimistic boost level!!
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

[Horizonblue]

Nice bodywork also.
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Euro 924, 1976

"If you can't fix it, don't break it"

/P.G. Andersen

[leadfoot]

Nice build mate, hope you're not putting too much faith in the stock cast pistons, they break ring lands pretty easily...
Details on the cooling system would be cool, is that another pump in the top centre of the pic??
P.S nice looking sc mount, is that your own creation or modelled of the db7??
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[morghen]

Very cool build !
Can you lower the boost and then rise it bit by bit?
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https://www.the924.com

[Rasta Monsta]

Requires swapping pulleys I think. . .
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Euro924S2]

hanks guys. The body work was done about 8 years ago now, with a 944 s2 replica nose supposedly made to fit the 924 but in reality it took weeks to get it fitting correctly. The side skirts are my own - I moulded plastic into the shape I wanted for the front and rear flares and used those to make fibre glass versions which I bonded on and then blended in with fibreglass filler. I'm still not happy with the S Zender rear valance as I think it looks too heavy from the side but I'm thinking of alternatives to that when I get time.

As for the engine, stu, you're spot on! That's a second stock pump driven off the same belt. Basically there are 2 coolant systems, how ever they are not separated from each other as a safety backup. Water enters the block from the stock pump, flows to the back of the block, exits the rear block core plug and comes in a 32mm pipe to the front of the engine bay, there it flows through a thermostat and once hot flows into a secondary radiator mounted in the front bumper (bottom right as you look from the front oft he car) the cooled water is then pumped by the second water pump through a 32mm pipe that runs parallel to the fuel rail to feed the back of the cylinder head with cool water (thermostat is 74*c) which then flows forward, through the front of the head and out through the stock thermostat and through the main radiator. The main rad is half the width of a stock one from a Honda civic type R and is all ally 52mm thick twin core. The secondary radiator is about 40cm x 15cm and 60mm thick triple core ally).

As for the pistons Stu, you make a very good point! Myself, Weasel and carrera RSR (Steve) have debated their strength over and over!! I have a set of Wossner forged pistons brand new on the shelf together with a block ready for them to go into, but I'm keen to see if stock ones will hold up if knock is prevented with a good tune using modern electronic control systems!?!

The piston failures I've heard about have largely been on big power applications but mostly using CIS or where a problem has caused a lean cylinder. I'm just about to fit a J&S Knocksense to hopefully help too.

The ring land thing is confusing though, since a lot have described ring breakage as a problem. And given the turbo rings are thinner than NA rings, they've machined the pistons to accept the thicker NA rings - therefore making the ring lands thinner still?? I guess only time will tell but even if I do bust them at least I'll know first hand what I did wrong / what caused it!

I'd be keen to hear your thoughts, knowledge and experiences on this though....

Cheers guys. John

[Euro924S2]

stu, the supercharger mounts are my own - made in cardboard first, then plywood - then finally in 10mm aluminium. It's bolted on with some old cylinder head bolts I had which were perfect diameter, but just needed the thread extending down the shank a little way!

As for boost, Rasta is right, I'd need a bigger nose pulley but I've already fitted the biggest I have which gives a ratio just below 2:1. I don't know what ratio the DB7 ran (I bought the charger under the impression it was for a Jag XJR 6, but sadly it's not - would be easier to replace if I break it from a jag compared to a DB7!)

Controlling the boost is pretty easy with the throttle though as unlike a turbo it's much more linear so I can, and have been limiting it to sub 1bar for the time being until it's tuned.

I'll try and post some engine build pics....

[Raceboy]

[Euro924S2]

Yes mate, that's the one. From the back I really like it, it adds depth and width by squaring off the bottom, but the shark fin sides don't really match any other lines on the car and looks a bit non-OEM which is somewhat ironic as it's one of the few parts on the car with a porsche part number!!! They were fitted to the last year of the 924S production cars to try and help them sell before the 944 took over completely.
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

[Cedric]

Your build is really nice! Although it looks a bit odd with the front The engine seems very well built and thought through. Will be interesting to see how this goes, I hope you will be up on the dyno soon !

Have you though about water/meth injection? Could be an alternative to lowering boost, and get really good detonation resistance.

If you run it on the safe side the pistons will probably last for a good while..

Will be interesting to see your experience on the J&S unit, just bought asecond hand one myself to replace the XS knocklite i use. Will hopefully be a great safety net..
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1980 924 Turbo
www.instagram.com/garagecedric/

[Euro924S2]

Rear core plug water outlet:


Exhaust gas temperature sensors. (NA manifold ported to match turbo head)


One radiator cut to make two!! The larger segment is for the charge cooler radiator and the smaller segment was rotated through 90 degrees with new end tanks and 32mm outlets and forms the new secondary radiator. The charge cooler radiator end tanks were redesigned and 19mm hose outlets fitted.



Schematic explaining my new coolant flow (in theory!!)


Water manifold for pluming of the secondary thermostat, heater matrix return hose and expansion tank feed.




Various parts I'd sandblasted and were waiting for me to powdercoat various shades of OEM looking grey!!



Modified brake booster bracket brings booster near the bulkhead giving more clearance to the charger, but needed a custom con rod making to lower the pedal back to a sensible height!



Before and after sand blasting...



First try at DIY powder coating!


Sandblasted 951 Brembo's


Powdercoated Brembo's



Re-painted engine bay with heat proofing!


Engine dry install...

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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

[Euro924S2]

Thanks Cedric, I bought a devils own water injection kit second hand but new in the box. My plan was to use it pre-charger if the charge cooler radiator was struggling to keep the temperatures down. I hadn't really thought of it for it's knock suppression qualities. I'm hoping the cooler running temps of the head, (low temp thermostats and coolant reroute) and the cooler EGT's by not having the backpressure of a turbo, plus my low air temps (less than 40*C) my knock limit might be reasonable. Certainly when I dyno'd the M62 at 1bar I wasn't knock limited. I did a run with my road tune map and then ran again with 4* more ingnition advance and gained 1bhp more, but no knock, then at 6* advance it knocked. Similarly retarding from my road map more than 2degrees lost me bhp. That was encouraging but in retrospect I was too rich for maximum power or ignition advance at approx 10.5:1. I was probably getting a cooling effect from the added fuel much like the water injection effect. This time I'll run a safe, but probably still not optimal 11:1 I think to gain a bit but without being too close to the edge!!

Out of interest, where to the ring lands break? (I'm wondering if I need to buy a boroscope to visually check things from time to time!)

I guess the front bumper isn't to everyone's taste but I really like the more modern lines of the smooth hipped 924 body but with the upto date 1 piece bumpers!
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp